Voltage distribution in transistor stacks using non-uniform transistor dimensions

ABSTRACT

A radio-frequency switch includes a first field-effect transistor having drain and source fingers separated by a first drain-to-source distance and a second field-effect transistor in a series connection with the first field-effect transistor, the second field-effect transistor having drain and source fingers separated by a second drain-to-source distance that is different than the first drain-to-source distance.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.15/240,771, filed Aug. 18, 2016, and entitled NON-UNIFORM SPACING INTRANSISTOR STACKS, which claims priority to U.S. Provisional ApplicationNo. 62/208,540, filed Aug. 21, 2015, and entitled NON-UNIFORM SPACING INTRANSISTOR STACKS, the disclosures of which are hereby incorporated byreference in its entirety.

BACKGROUND Field

The present disclosure generally relates to the field of electronics,and more particularly, to radio-frequency (RF) modules and devices.

Description of Related Art

In electronics applications, passive and active devices can be utilizedfor various purposes, such as for routing and/or processing ofradio-frequency (RF) signals in wireless devices.

SUMMARY

In some implementations, the present disclosure relates to afield-effect transistor stack comprising a first field-effect transistorhaving a source finger, a drain finger, and a gate finger interposedtherebetween, the source finger and the drain finger of the firstfield-effect transistor being separated by a first drain-to-sourcedistance, and a second field-effect transistor in a series connectionwith the first field-effect transistor, the second field-effecttransistor having a source finger, a drain finger, and a gate fingerinterposed therebetween, the source finger and the drain finger of thesecond field-effect transistor being separated by a seconddrain-to-source distance that is different than the firstdrain-to-source distance.

In certain embodiments, the second drain-to-source distance is greaterthan the first drain-to-source distance. The field-effect transistorstack may further comprise a third field-effect transistor in a seriesconnection with the second field-effect transistor, the thirdfield-effect transistor having a source finger, a drain finger, and agate finger interposed therebetween the source finger and the drainfinger of the third field-effect transistor being separated by a thirddrain-to-source distance that is different than both the first andsecond drain-to-source distances.

In certain embodiments, the first and second field-effect transistorsare silicon-on-insulator (SOI) transistors. The gate finger of the firstfield-effect transistor may have a gate width that is shorter than agate width of the gate finger of the second field-effect transistor. Incertain embodiments, the first field-effect transistor occupies asmaller physical area than the second field-effect transistor.

In some implementations, the present disclosure relates to afield-effect transistor stack comprising a first field-effect transistorhaving a first plurality of source fingers, a first plurality ofcorresponding drain fingers, and a first plurality of gate fingersincluding a gate finger disposed between each adjacent pair of sourceand drain fingers of the first plurality of drain fingers and the firstplurality of source fingers, a respective source finger and itscorresponding adjacent drain finger of the first field-effect transistorbeing separated by a first drain-to-source distance, and a secondfield-effect transistor in a series connection with the firstfield-effect transistor, the second field-effect transistor having asecond plurality of source fingers, a second plurality of correspondingdrain fingers, and a second plurality of gate fingers including a gatefinger disposed between each adjacent pair of source and drain fingersof the second plurality of drain fingers and the second plurality ofsource fingers, a respective source finger and its correspondingadjacent drain finger of the second field-effect transistor beingseparated by a second drain-to-source distance that is different thanthe first drain-to-source distance. In certain embodiments, the seconddrain-to-source distance is greater than the first drain-to-sourcedistance.

The field-effect transistor stack may further comprise a thirdfield-effect transistor in a series connection with the secondfield-effect transistor, the third field-effect transistor having athird plurality of source fingers, a third plurality of correspondingdrain fingers, and a third plurality of gate fingers including a gatefinger disposed between each adjacent pair of source and drain fingersof the third plurality of drain fingers and the third plurality ofsource fingers, a respective source finger and its correspondingadjacent drain finger of the third field-effect transistor beingseparated by a third drain-to-source distance that is different thanboth the first and second drain-to-source distances. In certainembodiments, the second plurality of gate fingers has a gate width thatis longer than a gate width of the first plurality of gate fingers andshorter than a gate width of the third plurality of gate fingers. Thefield-effect transistor stack may further comprise a fourth field-effecttransistor in a series connection with the third field-effecttransistor, the fourth field-effect transistor having a fourth pluralityof source fingers, a fourth plurality of corresponding drain fingers,and a fourth plurality of gate fingers including a gate finger disposedbetween each adjacent pair of source and drain fingers of the fourthplurality of drain fingers and the fourth plurality of source fingers, arespective source finger and its corresponding adjacent drain finger ofthe fourth field-effect transistor being separated by a fourthdrain-to-source distance that is equal to third distance.

In certain embodiments, the first plurality of gate fingers comprisesmore gate fingers than the second plurality of gate fingers. The firstplurality of gate fingers may have a first gate width that is shorterthan a gate width of the second plurality of gate fingers. The firstfield-effect transistor may have a total periphery that is greater thana total periphery of the second field-effect transistor. In certainembodiments, the first field-effect transistor has a first plurality ofdrain fingers having second level metal traces electrically coupledthereto to provide added capacitance. The first field-effect transistormay occupy a smaller physical area than the second field-effecttransistor. The first field-effect transistor may have a physical areaequal to a physical area of the second field-effect transistor.

In some implementations, the present disclosure relates to a transistorstack comprising a plurality of field-effect transistors connected inseries, a first field-effect transistor of the plurality of field-effecttransistors having a first drain-to-source spacing, and a secondfield-effect transistor of the plurality of field-effect transistorsconnected in series with the first field-effect transistor, the secondfield-effect transistor having a second drain-to-source spacing that isgreater than the first drain-to-source spacing. The transistor stack mayfurther comprise a third field-effect transistor of the plurality offield-effect transistors having a third drain-to-source spacing that isgreater than the second drain-to-source spacing. In certain embodiments,the first field-effect transistor has a gate width that is shorter thana gate width of the second field-effect transistor.

In some implementations, the present disclosure relates to a method forfabricating a radio-frequency (RF) device. The method may compriseproviding a semiconductor substrate, forming a first field-effecttransistor (FET) over the semiconductor substrate, the first FET havinga first plurality of gate fingers separated by a first gate-to-gatedistance, and forming a second FET over the semiconductor substrate in aseries connection with the first FET, the second FET having a secondplurality of gate fingers separated by a second gate-to-gate distance,the second gate-to-gate distance being greater than the firstgate-to-gate distance.

In certain embodiments, the first and second FETs aresilicon-on-insulator (SOI) transistors. The first plurality of gatefingers may be more than the second plurality of gate fingers. The firstplurality of gate fingers may have a first gate width that is shorterthan a gate width of the second plurality of gate fingers. In certainembodiments, the first FET has a total periphery that is greater than atotal periphery of the second FET. The first FET may have a totalperiphery that is greater than a total periphery of the second FET. Incertain embodiments, the first FET has a first plurality of drainfingers having second level metal traces electrically coupled thereto toprovide added capacitance. The first FET may occupy a smaller physicalarea than the second FET.

In certain embodiments, the method further comprises a third FET havinga third plurality of gate fingers separated by a third gate-to-gatedistance that is greater than the second gate-to-gate distance. Thesecond plurality of gate fingers may have a gate width that is longerthan a gate width of the first plurality of gate fingers and shorterthan a gate width of the third plurality of gate fingers.

In some implementations, the present disclosure relates to aradio-frequency (RF) module comprising a packaging substrate configuredto receive a plurality of devices, and a transistor stack mounted on thepackaging substrate, the transistor stack including a first field-effecttransistor (FET) disposed on the substrate, the first FET having a firstplurality of gate fingers separated by a first gate-to-gate distance,and a second FET disposed on the semiconductor substrate in a seriesconnection with the first FET, the second FET having a second pluralityof gate fingers separated by a second gate-to-gate distance, the secondgate-to-gate distance being greater than the first gate-to-gatedistance.

In certain embodiments, the first and second FETs aresilicon-on-insulator (SOI) transistors. The first plurality of gatefingers may be more than the second plurality of gate fingers. The firstplurality of gate fingers may have a first gate width that is shorterthan a gate width of the second plurality of gate fingers. The first FETmay have a total periphery that is greater than a total periphery of thesecond FET. In certain embodiments, the first FET has a total peripherythat is greater than a total periphery of the second FET. The first FETmay have a first plurality of drain fingers having second level metaltraces electrically coupled thereto to provide added capacitance. Thefirst FET may occupy a smaller physical area than the second FET. Incertain embodiments, the RF module further comprises a third FET havinga third plurality of gate fingers separated by a third gate-to-gatedistance that is greater than the second gate-to-gate distance. Thesecond plurality of gate fingers may have a gate width that is longerthan a gate width of the first plurality of gate fingers and shorterthan a gate width of the third plurality of gate fingers.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are depicted in the accompanying drawings forillustrative purposes, and should in no way be interpreted as limitingthe scope of the inventions. In addition, various features of differentdisclosed embodiments can be combined to form additional embodiments,which are part of this disclosure. Throughout the drawings, referencenumbers may be reused to indicate correspondence between referenceelements.

FIG. 1 shows an example of a field-effect transistor (FET) device havingan active FET implemented on a substrate, and a region below the activeFET configured to include one or more features to provide one or moredesirable operating functionalities for the active FET.

FIG. 2 shows an example of a FET device having an active FET implementedon a substrate, and a region above the active FET configured to includeone or more features to provide one or more desirable operatingfunctionalities for the active FET.

FIG. 3 shows that in some embodiments, a FET device can include both ofthe regions of FIGS. 1 and 2 relative to an active FET.

FIG. 4 shows an example FET device implemented as an individualsilicon-on-insulator (SOI) unit.

FIG. 5 shows that in some embodiments, a plurality of individual SOIdevices similar to the example SOI device of FIG. 4 can be implementedon a wafer.

FIG. 6A shows an example wafer assembly having a first wafer and asecond wafer positioned over the first wafer.

FIG. 6B shows an unassembled view of the first and second wafers of theexample of FIG. 6A.

FIG. 7A shows a terminal representation of an SOI FET according to oneor more embodiments.

FIG. 7B shows a FET device according to one or more embodiments.

FIGS. 8A and 8B show side sectional and plan views, respectively, of anexample SOI FET device according to one or more embodiments.

FIG. 9 shows a side sectional view of an SOI substrate that can beutilized to form an SOI FET device according to one or more embodiments.

FIG. 10 shows a side sectional view of an SOI FET device according toone or more embodiments.

FIG. 11 shows a process that can be implemented to facilitatefabrication of an SOI FET device having one or more features asdescribed herein.

FIG. 12 shows examples of various stages of the fabrication process ofFIG. 11.

FIG. 13 shows an example of a radio-frequency (RF) switchingconfiguration having an RF core and an energy management (EM) core.

FIG. 14 shows an example of the RF core of FIG. 13, in which each of theswitch arms includes a stack of FET devices.

FIG. 15 shows an example biasing configuration implemented in a switcharm having a stack of FETs.

FIG. 16 shows an example of an RF core according to one or moreembodiments.

FIG. 17 shows an example of an RF core according to one or moreembodiments.

FIG. 18 is a graph illustrating possible drain-to-source voltages acrosstransistors in a transistor stack according to one or more embodiments.

FIG. 19 shows an example of an RF core according to one or moreembodiments.

FIG. 20A shows a plan view of an example transistor stack according toone or more embodiments.

FIG. 20B shows a side view of an example FET transistor according to oneor more embodiments.

FIG. 20C shows a schematic depiction of the transistor stack of FIG. 20Aaccording to one or more embodiments.

FIG. 21A shows a plan view of an example transistor stack according toone or more embodiments.

FIG. 21B shows a side view of an example FET transistor according to oneor more embodiments.

FIG. 21C shows a schematic depiction of the transistor stack of FIG. 21Aaccording to one or more embodiments.

FIG. 22A shows a plan view of an example transistor stack according toone or more embodiments.

FIG. 22B shows a side view of an example FET transistor according to oneor more embodiments.

FIG. 22C shows a schematic depiction of the transistor stack of FIG. 22Aaccording to one or more embodiments.

FIG. 23 shows a plan view of an example transistor stack according toone or more embodiments.

FIG. 24 shows a switch assembly implemented in asingle-pole-single-throw (SPST) configuration utilizing an SOI FETdevice.

FIG. 25 shows that in some embodiments, the SOI FET device of FIG. 24can include a substrate biasing/coupling feature as described herein.

FIG. 26 shows an example of how two SPST switches having one or morefeatures as described herein can be utilized to form a switch assemblyhaving a single-pole-double-throw (SPDT) configuration.

FIG. 27 shows that the switch assembly of FIG. 26 can be utilized in anantenna switch configuration.

FIG. 28 shows an example of how three SPST switches having one or morefeatures as described herein can be utilized to form a switch assemblyhaving a single-pole-triple-throw (SP3T) configuration.

FIG. 29 shows that the switch assembly of FIG. 28 can be utilized in anantenna switch configuration.

FIG. 30 shows an example of how four SPST switches having one or morefeatures as described herein can be utilized to form a switch assemblyhaving a double-pole-double-throw (DPDT) configuration.

FIG. 31 shows that the switch assembly of FIG. 30 can be utilized in anantenna switch configuration.

FIG. 32 shows an example of how nine SPST switches having one or morefeatures as described herein can be utilized to form a switch assemblyhaving a 3-pole-3-throw (3P3T) configuration.

FIG. 33 shows that the switch assembly of FIG. 32 can be utilized in anantenna switch configuration.

FIGS. 34A-34E show examples of how a DPDT switching configuration can beoperated to provide different signal routing functionalities.

FIGS. 35A and 35B show plan and side views, respectively, of a packagedmodule having one or more features as described herein.

FIG. 36 shows a schematic diagram of an example switching configurationthat can be implemented in a module according to one or moreembodiments.

FIG. 37 depicts an example wireless device having one or moreadvantageous features described herein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein are for convenience only and do notnecessarily affect the scope or meaning of the claimed invention.

Introduction

Disclosed herein are various examples of a field-effect transistor (FET)device having one or more regions relative to an active FET portionconfigured to provide a desired operating condition for the active FET.In such various examples, terms such as FET device, active FET portion,and FET are sometimes used interchangeably, with each other, or somecombination thereof. Accordingly, such interchangeable usage of termsshould be understood in appropriate contexts.

FIG. 1 shows an example of a FET device 100 having an active FET 101implemented on a substrate 103. As described herein, such a substratecan include one or more layers configured to facilitate, for example,operating functionality of the active FET, processing functionality forfabrication and support of the active FET, etc. For example, if the FETdevice 100 is implemented as a silicon-on-Insulator (SOI) device, thesubstrate 103 can include an insulator layer such as a buried oxide(BOX) layer, an interface layer, and a handle wafer layer.

FIG. 1 further shows that in some embodiments, a region 105 below theactive FET 101 can be configured to include one or more features toprovide one or more desirable operating functionalities for the activeFET 101. For the purpose of description, it will be understood thatrelative positions above and below are in the example context of theactive FET 101 being oriented above the substrate 103 as shown.Accordingly, some or all of the region 105 can be implemented within thesubstrate 103. Further, it will be understood that the region 105 may ormay not overlap with the active FET 101 when viewed from above (e.g., ina plan view).

FIG. 2 shows an example of a FET device 100 having an active FET 101implemented on a substrate 103. As described herein, such a substratecan include one or more layers configured to facilitate, for example,operating functionality of the active FET 100, processing functionalityfor fabrication and support of the active FET 100, etc. For example, ifthe FET device 100 is implemented as a silicon-on-Insulator (SOI)device, the substrate 103 can include an insulator layer such as aburied oxide (BOX) layer, an interface layer, and a handle wafer layer.

In the example of FIG. 2, the FET device 100 is shown to further includean upper layer 107 implemented over the substrate 103. In someembodiments, such an upper layer can include, for example, a pluralityof layers of metal routing features and dielectric layers to facilitate,for example, connectivity functionality for the active FET 100.

FIG. 2 further shows that in some embodiments, a region 109 above theactive FET 101 can be configured to include one or more features toprovide one or more desirable operating functionalities for the activeFET 101. Accordingly, some or all of the region 109 can be implementedwithin the upper layer 107. Further, it will be understood that theregion 109 may or may not overlap with the active FET 101 when viewedfrom above (e.g., in a plan view).

FIG. 3 shows an example of a FET device 100 having an active FET 101implemented on a substrate 103, and also having an upper layer 107. Insome embodiments, the substrate 103 can include a region 105 similar tothe example of FIG. 1, and the upper layer 107 can include a region 109similar to the example of FIG. 2.

Examples related to some or all of the configurations of FIGS. 1-3 aredescribed herein in greater detail.

In the examples of FIGS. 1-3, the FET devices 100 are depicted as beingindividual units (e.g., as semiconductor die). FIGS. 4-6 show that insome embodiments, a plurality of FET devices having one or more featuresas described herein can be fabricated partially or fully in a waferformat, and then be singulated to provide such individual units.

For example, FIG. 4 shows an example FET device 100 implemented as anindividual SOI unit. Such an individual SOI device can include one ormore active FETs 101 implemented over an insulator such as a BOX layer104 which is itself implemented over a handle layer such as a silicon(Si) substrate handle wafer 106. In the example of FIG. 4, the BOX layer104 and the Si substrate handle wafer 106 can collectively form thesubstrate 103 of the examples of FIGS. 1-3, with or without thecorresponding region 105.

In the example of FIG. 4, the individual SOI device 100 is shown tofurther include an upper layer 107. In some embodiments, such an upperlayer can be the upper layer 103 of FIGS. 2 and 3, with or without thecorresponding region 109.

FIG. 5 shows that in some embodiments, a plurality of individual SOIdevices similar to the example SOI device 100 of FIG. 4 can beimplemented on a wafer 200. As shown, such a wafer can include a wafersubstrate 103 that includes a BOX layer 104 and a Si handle wafer layer106 as described in reference to FIG. 4. As described herein, one ormore active FETs can be implemented over such a wafer substrate.

In the example of FIG. 5, the SOI device 100 is shown without the upperlayer (107 in FIG. 4). It will be understood that such a layer can beformed over the wafer substrate 103, be part of a second wafer, or anycombination thereof.

FIG. 6A shows an example wafer assembly 204 having a first wafer 200 anda second wafer 202 positioned over the first wafer 200. FIG. 6B shows anunassembled view of the first and second wafers 200, 202 of the exampleof FIG. 6A.

In some embodiments, the first wafer 200 can be similar to the wafer 200of FIG. 5. Accordingly, the first wafer 200 can include a plurality ofSOI devices 100 such as the example of FIG. 4. In some embodiments, thesecond wafer 202 can be configured to provide, for example, a region(e.g., 109 in FIGS. 2 and 3) over a FET of each SOI device 100, and/orto provide temporary or permanent handling wafer functionality forprocess steps involving the first wafer 200.

Examples of SOI Implementation of FET Devices

Certain embodiments disclosed herein provide for performance and/or sizeimprovement in transistor stacks using non-uniform drain-to-sourcespacing and/or other dimensional modifications. Principles and conceptsdisclosed herein may advantageously be implemented in connection withSilicon-on-Insulator (SOI) processes. Although certain embodiments aredisclosed herein in the context of SOI technologies, it should beunderstood that the principles disclosed herein may be applicable toother transistor technologies as well.

SOI process technology is utilized in many radio-frequency (RF)circuits, including, for example, those involving high performance, lowloss, high linearity switches. In such RF switching devices, performanceadvantage typically results from building a transistor in silicon, whichsits on an insulator such as an insulating buried oxide (BOX). The BOXtypically sits on a handle wafer, typically silicon, but can be glass,borosilicon glass, fused quartz, sapphire, silicon carbide, or any otherelectrically-insulating material.

An SOI transistor is viewed as a 4-terminal field-effect transistor(FET) device with gate, drain, source, and body terminals; oralternatively, as a 5-terminal device, with an addition of a substratenode. Such a substrate node can be biased and/or be coupled one or moreother nodes of the transistor to, for example, improve linearity and/orloss performance of the transistor. Various examples related to SOIand/or other semiconductor active and/or passive devices are describedherein in greater detail. Although various examples are described in thecontext of RF switches, it will be understood that one or more featuresof the present disclosure can also be implemented in other applicationsinvolving FETs and/or other semiconductor devices.

FIG. 7A shows an example 4-terminal representation of an SOI FET 100having nodes associated with a gate, a source, a drain and a body. Itwill be understood that in some embodiments, the source and the drainnodes can be reversed.

FIG. 7B shows that in some embodiments, an SOI FET 150 having one ormore features as described herein can have its gate node biased by agate bias network 156, its body node biased by a body bias network 154and/or one or more additional nodes biased by a bias network. Examplesrelated to such gate and body bias networks are described in U.S. Pub.No. 2014/0009274, titled “Circuits, Devices, Methods and ApplicationsRelated to Silicon-on-Insulator Based Radio-Frequency Switches,” whichis hereby incorporated by reference in its entirety.

FIGS. 8A and 8B show side sectional and plan views of an example SOI FET100. The substrate of the FET 100 can be, for example, a siliconsubstrate associated with a handle wafer 106. Although described in thecontext of such a handle wafer, it will be understood that the substratedoes not necessarily need to have material composition and/orfunctionality generally associated with a handle wafer. Furthermore,handle wafer and/or other substrate layers like that shown in FIG. 8Amay be referred to herein as “bulk substrate,” “bulk silicon,” “handlesubstrate,” “stabilizing substrate,” or the like, and may comprise anysuitable or desirable material, depending on the application.

An insulator layer such as a buried oxide (BOX) layer 104 is shown to beformed over the handle wafer 106, and a FET structure is shown to beformed in an active silicon device 102 over the BOX layer 104. Invarious examples described herein, and as shown in FIGS. 8A and 8B, theFET structure can be configured as an NPN or PNP device.

In the examples of FIGS. 8A and 8B, terminals for the gate, source,drain and body are shown to be configured and provided so as to allowoperation of the FET. The BOX layer 104 may be formed on thesemiconductor substrate 106. In certain embodiments, the BOX layer 104can be formed from materials such as silicon dioxide or sapphire. Sourceand drain may be p-doped (or n-doped) regions whose exposed surfacesgenerally define rectangles. Source/drain regions can be configured sothat source and drain functionalities are reversed. FIGS. 8A and 8Bfurther show that a gate can be formed so as to be positioned betweenthe source and the drain. The example gate is depicted as having arectangular shape that extends along with the source and the drain. TheFET 100 may further include a body contact. Electrically conductivefeatures such as conductive vias and/or trenches may be used to connectto the drain, source, gate and/or body terminals of the FET in certainembodiments. Various examples of how such an electrically conductivefeature can be implemented are described herein in greater detail.

Formations of the source and drain regions, and/or the body contact canbe achieved by a number of known techniques. In some embodiments, thesource and drain regions can be formed adjacent to the ends of theirrespective upper insulator layers, and the junctions between the bodyand the source/drain regions on the opposing sides of the body canextend substantially all the way down to the top of the buried oxidelayer. Such a configuration can provide, for example, reducedsource/drain junction capacitance. To form a body contact for such aconfiguration, an additional gate region can be provided.

FIG. 9 shows a side sectional view of an SOI substrate 10 that can beutilized to form an SOI FET 100, as shown in FIG. 10, which may have anelectrical connection for a substrate layer 106 (e.g., Si handle layer).In FIG. 9, an insulator layer such as a BOX layer 104 is shown to beformed over the Si handle layer 106. An active Si layer 12 is shown tobe formed over the BOX layer 104.

In FIG. 10, an active Si device 102 is shown to be formed from theactive Si layer 12 of FIG. 9. The device 100 includes a metal stack 110,which may facilitate electrical contact with the active Si device (e.g.,a FET). In some embodiments, such a metal stack 110 can allow forcertain conductive features of the FET 100 to be electrically connectedto a terminal 112, or other electrically-coupled element. In the exampleof FIG. 10, a passivation layer 114 can be formed to cover some or allof the connections/metal stack 110 and/or active device 102.

In some embodiments, a trap-rich layer 14 can be implemented between theBOX layer 104 and the Si handle layer 106. In certain embodiments, anelectrical connection to the Si handle layer 106 through one or moreconductive feature(s) (e.g., substrate contact; not shown in theembodiment of FIG. 10) can eliminate or reduce the need for such atrap-rich layer, which is typically present to control charge at aninterface between the BOX layer 104 and the Si handle layer 106, and caninvolve relatively costly process steps.

FIG. 11 shows a process 130 that can be implemented to fabricate an SOIFET having one or more features as described herein. FIG. 12 showsexamples of various stages/structures associated with the various stepsof the fabrication process of FIG. 11.

In block 132 of FIG. 11, an SOI substrate can be formed or provided. Instate 140 of FIG. 12, such an SOI substrate can include an Si substrate106 such as an Si handle layer, an oxide layer 104 over the Si substrate106, and an active Si layer 12 over the oxide layer 104. Such an SOIsubstrate may or may not have a trap-rich layer between the oxide layer104 and the Si substrate 106.

In block 134 of FIG. 11, one or more FETs can be formed with the activeSi layer. In state 142 of FIG. 12, such FET(s) is depicted as 150.

In the example of FIGS. 11 and 12, it will be understood that thevarious blocks of the process 130 may or may not be performed in theexample sequence shown. In some embodiments, conductive feature(s) suchas one or more deep trenches can be formed and filled with poly prior tothe formation of the FET(s). In some embodiments, such conductivefeature(s) can be formed (e.g., cut and filled with a metal such astungsten (W) after the formation of the FET(s). It will be understoodthat other variations in sequences associated with the example of FIGS.11 and 12 can also be implemented.

In block 136 of FIG. 11, electrical connections can be formed for theFET(s). In state 146 of FIG. 12, such electrical connections aredepicted as a metallization stack collectively identified by referencenumber 110. Such a metal stack 110 can electrically connect the FET(s)150 to one or more terminals 112, or other electrical element or device(e.g., active or passive device). In the example state 146 of FIG. 12, apassivation layer 114 is shown to be formed to cover some or all of theconnections/metallization stack 110 and/or FET(s) 150.

FIGS. 13-15 show that in some embodiments, SOI FETs having one or morefeatures as described herein can be implemented in RF switchingapplications.

FIG. 13 shows an example of an RF switching configuration 160 having anRF core 162 and an energy management (EM) core 164. Additional detailsconcerning such RF and EM cores are described in U.S. Pub. No.2014/0009274, titled “Circuits, Devices, Methods and ApplicationsRelated to Silicon-on-Insulator Based Radio-Frequency Switches,” whichis incorporated by reference herein in its entirety. The example RF core162 of FIG. 13 is shown as a single-pole-double-throw (SPDT)configuration in which series arms of transistors 100 a, 100 b arearranged between a pole and first and second throws, respectively. Nodesassociated with the first and second throws are shown to be coupled toground through their respective shunt arms of transistors 100 c, 100 d.

In the example of FIG. 13, the transistors between the pole node and thetwo throw nodes are depicted as single transistors. In someimplementations, such switching functionalities between the pole(s) andthe throw(s) can be provided by switch arm segments, where each switcharm segment includes a plurality of transistors such as FETs.

An example RF core configuration 830 of an RF core having such switcharm segments is shown in FIG. 14. In the example, the pole 802 a and thefirst throw node 804 a are shown to be coupled via a first switch armsegment 840 a. Similarly, the pole 802 a and the second throw node 804 bare shown to be coupled via a second switch arm segment 840 b. The firstthrow node 804 a is shown to be capable of being shunted to an RF groundvia a first shunt arm segment 842 a. Similarly, the second throw node804 b is shown to be capable of being shunted to the RF ground via asecond shunt arm segment 842 b.

In an example operation, when the RF core 830 is in a state where an RFsignal is being passed between the pole 802 a and the first throw node804 a, all of the FETs in the first switch arm segment 840 a can be inan ON state, and all of the FETs in the second switch arm segment 804 bcan be in an OFF state. The first shunt arm 842 a for the first thrownode 804 a can have all of its FETs in an OFF state so that the RFsignal is not shunted to ground as it travels from the pole 802 a to thefirst throw node 804 a. All of the FETs in the second shunt arm 842 bassociated with the second throw node 804 b can be in an ON state sothat any RF signals or noise arriving at the RF core 830 through thesecond throw node 804 b is shunted to the ground so as to reduceundesirable interference effects to the pole-to-first-throw operation.

Again, although described in the context of an SP2T configuration, itwill be understood that RF cores having other numbers of poles andthrows can also be implemented.

In some implementations, a switch arm segment (e.g., 840 a, 840 b, 842a, 842 b) can include one or more semiconductor transistors such asFETs. In some embodiments, an FET may be capable of being in a firststate or a second state and can include a gate, a drain, a source, and abody (sometimes also referred to as a substrate). In some embodiments,an FET can include a metal-oxide-semiconductor field-effect transistor(MOSFET). In some embodiments, one or more FETs can be connected inseries forming a first end and a second end such that an RF signal canbe routed between the first end and the second end when the FETs are ina first state (e.g., ON state). In the example shown in FIG. 15, thegate of each of the FETs 920 in a switch arm 940 can be connected to agate bias/coupling circuit to receive a gate bias signal and/or couplethe gate to another part of the FET 920 or the switch arm 940. In someimplementations, designs or features of the gate bias/couplingcircuit(s) (e.g., 150 a) can improve performance of the switch arm 940.Such improvements in performance can include, but are not limited to,device insertion loss, isolation performance, power handling capabilityand/or switching device linearity.

Non-Uniform Drain-to-Source Spacing

Parasitic capacitance to ground may be a factor of transistor layout,oxide thickness, and/or substrate thickness. Certain embodimentsdisclosed herein provide systems and processes for compensating forperformance degradation due to parasitic capacitance in transistorstacks through the use of non-uniform drain-to-source spacing and/orother dimensional modifications to provide non-uniform capacitanceacross stack devices. Such features may provide improved performanceand/or reduction in size for transistors compared to certainconventional transistor devices. The non-uniform drain-to-source spacingembodiments disclosed herein may be applicable to any FET-basedtechnology, such as SOI, CMOS, PHEMT, MESFET, or other FET or transistortype. Furthermore, transistor stacks configured with non-uniformdrain-to-source spacing may be applicable to switching, amplifying,mixing, or other applications or solutions applications. Drain-to-sourcespacing in transistor devices is discussed herein in connection withvarious embodiments and benefits. In certain embodiments, modifyingdrain-to-source spacing in a transistor can be correlated withcorresponding modification in gate-to-gate spacing between adjacent gatefingers of a transistor. Therefore, discussion and references herein todrain-to-source spacing reduction or other modification should beunderstood to possibly correspond to similar reduction or modificationto gate-to-gate spacing. For example, in certain embodiments,drain-to-source spacing in a transistor may be substantially equal togate-to-gate spacing within the transistor. In certain embodiments,reduction or modification in drain-to-source spacing in a transistor isproportional to reduction or modification in gate-to-gate spacing.Furthermore, relative difference in drain-to-source spacing of differenttransistors in a transistor stack may correspond with relativedifference in gate-to-gate spacing of the transistors in the transistorstack. In certain embodiments, the relative difference indrain-to-source spacing of different transistors in a transistor stackis proportional to the relative difference of gate-to-gate spacing ofthe transistors in the transistor stack.

FIG. 16 shows an example of a radio-frequency (RF) core 1062 accordingto one or more embodiments. The circuit 1062 is illustrated as asingle-pole-double-throw (SPDT) switch. However, one having ordinaryskill in the art will appreciate that principles and features disclosedherein may be applicable in other types of circuits or devices.

The RF core 1062 includes multiple transistors (e.g., FETs) 1000 a in aseries stack, which may be utilized to provide relatively high-voltagehandling and/or high-linearity performance for one or more applications.The transistor stack 1000 a may include a plurality of transistors sothat the relatively high voltage may be handled by lower-voltagetransistors. That is, the RF voltage present at the pole may be greaterthan a single transistor may be configured to handle. FETs and/or othertransistor devices may suffer from certain parasitic capacitances due tothe underlying substrate (C_(sub)) under various conditions. Forexample, parasitic capacitance between a drain/source well and groundmay be present in SOI and/or other processes. Such parasitic capacitancemay be affected by various factors, such as transistor area, oxidethickness, bulk substrate type, and/or the like.

FIG. 17 shows an example of a radio-frequency (RF) core 1162 accordingto one or more embodiments. Certain parasitic capacitances associatedwith the various transistor devices is illustrated in the diagram ofFIG. 17. Each FET of a transistor stack (e.g., series or shunt stack)may have a parasitic capacitance to ground. For example, the illustratedcapacitance C₁ may represent a parasitic capacitance associated with Q₁and/or Q₂. In certain embodiments, each transistor in a transistor stackmay be a similar parasitic capacitance to ground. It may generally notbe possible to eliminate or decrease the parasitic capacitance throughthe box layer of an SOI device to the backside wafer, and socompensation for such capacitance may be desirable in certain processes.

In certain embodiments, the parasitic capacitance associated with afirst transistor in a stack may have a relatively more detrimentaleffect on the performance of the associated transistor than the effectof parasitic capacitance on a following transistor in the stack; forexample, the capacitance C₁ may have a more detrimental effect ontransistor Q₁ than capacitance C₅ has on transistor Q₅. This may be duein part to the RF voltage present at the gate of Q₁ being greater thanat gates of subsequent transistors that are closer to ground. Therefore,due to the uneven effect of capacitance on the various transistors,uneven voltage division may occur across the stack of transistors.

FIG. 18 is a graph illustrating possible drain-to-source voltages acrosstransistors in a transistor stack according to one or more embodiments.The graph of FIG. 18 provides an example of simulated data whererelative voltage drop at each of the FETs is plotted against the FETnumber along the stack. For example, there may be a voltage drop ofabout 0.135 of the input voltage (5V in this example) across a first FETin a transistor stack, about 0.118 of the input voltage across a secondFET, and so on.

In FIG. 18, one can readily see that there can be significant imbalanceof voltage drop values along the stack. It should be understood that forother configurations and architectures having constant gate width,voltage imbalances may also be similar to, the example of FIG. 18. Suchvoltage imbalances may or may not closely follow the example of FIG. 18,but the general trend is typically similar, where the first FET (wherethe power is incident) is typically the limiting factor with the highestvoltage drop. As described herein, such an uneven voltage distributionalong the stack can result in degradation of switch performance withrespect to, for example, harmonic peaking, compression point and/orintermodulation distortion (IMD). Also, at higher power levels, thefirst FET can go into breakdown before other FETs, thereby limiting theoverall performance of the switch.

It is further noted that such an uneven voltage distribution can impactthe breakdown voltage performance of the stack. For example, supposethat an input voltage of 5V is provided at an input of a stack having 10FETs, and that voltage drop across each FET is substantially constant(e.g., 0.1 of the input voltage, or 0.5V, for the 10-FET example) sothat there is no voltage imbalance within the stack. Also assume thateach FET is capable of handling at least the example 5V without breakingdown. Since each FET can handle 5V, and since there is no voltageimbalance, one can expect that the example stack as a whole can handle10 times 5V, or 50V.

In a stack with an uneven voltage distribution, one can expect that aFET with the highest relative voltage drop will break down first whenthe input voltage is increased, thereby yielding a weak link within thestack. In the example of FIG. 18, such a weak link may be the first FET,which has the highest relative voltage drop value of approximately0.135. Accordingly, a degraded breakdown voltage Vb for the examplestack of FIG. 18 can be estimated by scaling the input voltage (e.g.,5V) with the highest relative voltage drop value (0.135), as 5/0.135, orapproximately 37V. Compared to the foregoing example of 50V for theconstant-voltage drop (among the FETs), 37V is a significant reductionin voltage handling capability of the example stack represented in FIG.18.

In view of the negative effects of uneven voltage distribution asillustrated in FIG. 18, it may be desirable to implement features thatpromote more even voltage distribution across a transistor stack, whichmay ultimately result in more total voltage across the whole stackbefore any one of the transistors breaks down. The effect of unevenvoltage distribution may be at least partially mitigated by addingdrain-to-source fixed capacitance on one or more (but not all) of thetransistors of the stack, such as on one or more transistors thatexperience relatively higher voltage levels; adding capacitance acrossdrain-to-source may at least partially reduce the drain-to-sourcevoltage for a respective transistor, which may promote more even voltagedistribution across all transistors (e.g., FETs) in the stack. Certainsystems and methods for compensating for uneven voltage distribution intransistor stacks are disclosed herein, as well as in U.S. Pub. No.2015/0041917, titled “Field-Effect Transistor Stack VoltageCompensation,” filed on Aug. 4, 2014, the disclosure of which is herebyexpressly incorporated by reference herein in its entirety.

Selective addition of capacitance to one or more transistors of thestack may be achieved in various ways. FIG. 19 shows an example of aradio-frequency (RF) core according to one or more embodiments, whereinone or more transistors of a series or shunt transistor stack is atleast partially bypassed by adding a drain-to-source capacitance. Thecapacitors (C_(1a), C_(2a), C_(1c), C_(2c)) may at least partiallycompensate for uneven RF voltage distribution across the respectivetransistor stacks. For example, with respect to the series stackincluding transistors Q_(1a)-Q_(6a), the collective RF voltages acrossthe stack may become at least partially more uniform in the presence ofthe added capacitors C_(1a) and C_(2a). In certain embodiments, addingone or more drain-to-source capacitors may allow for some or all of thetransistors of the stack to have similar voltages, which may allow for arelatively higher total voltage-handling and/or linearity performancecapability for the stack.

In certain embodiments, a first capacitor C_(1a) of the stack may beassociated with a capacitor with a higher capacitance value than one ormore capacitors (e.g., C_(2a)) associated with subsequent transistor(s)(e.g., Q_(2a)) of the stack. Although the illustrated embodiment of FIG.19 only shows capacitors (C_(1a), C_(2a)) associated with the first twotransistors (Q_(1a), Q_(2a)) of the series stack 1300 a, it should beunderstood that any number or selection of transistors of the stack maybe at least partially bypassed by added capacitance in certainembodiments. Where only a subset of transistors is associated with addedcapacitance, such capacitance may advantageously be associated withfront-side transistors.

Added capacitance on selected transistors may be accomplished by addingfixed metal-insulator-metal (MIM) (e.g., lumped element MIMcapacitor(s)) capacitors to drain and source nodes of the respectivetransistors. Additionally or alternatively, capacitance may be achievedby adding additional metal to the respective transistor fingers, therebyproviding interdigitated capacitor(s).

Generally, added drain-to-source capacitance, as described above, may beimplemented in connection with transistor stacks comprising transistorshaving uniform drain-to-source spacing. For example, transistors such asFETs may be laid out with drain-to-source spacing that is generallylarger than manufacturing standard requirements in order to maintainrelatively low capacitance, which may be desirable in certain respectsfor at least some transistors of the stack. However, such uniformdrain-to-source spacing can lead to the uneven voltage distributionissues described above. Certain embodiments disclosed herein provideimproved voltage distribution across transistor stacks by creatinghigher capacitance for at least one of the top/front transistors in thestack at least in part by changing the actual transistor drain-to-sourcedistance for selected transistors relative to other transistor(s) of thestack, which may be correlated with change in gate-to-gate distancebetween adjacent gate fingers, as explained above.

The method of adding additional drain-to-source capacitance usingnon-uniform drain-to-source spacing may provide certain benefits intransistor stacks over those having uniform drain-to-source distances,such as reduced size, and/or lower resistance, which may decrease RFlosses. In certain embodiments, only a subset of transistors of a stackmay have added capacitance from modified drain-to-source (and/orgate-to-gate) spacing, wherein spacing is designed to provide decreasingcapacitance values in one direction, such as in a direction of signaltransmission. For example, C_(1a) and/or C_(1c) may have highercapacitance values than subsequent transistors C_(2a) and/or C_(2c),respectively. In an embodiment, a transistor stack implementingnon-uniform drain-to-source (and/or gate-to-gate) spacing may compriseapproximately twelve transistors, wherein a subset of transistors, suchas approximately four, may have added capacitance. In an embodiment,capacitance is added to each of the transistors of the stack with theexception of the last transistor.

FIG. 20A shows a plan view of an example transistor stack according toone or more embodiments. The transistor stack illustrated in FIG. 20Aincludes four transistors (Q₁-Q₄), each with a certain number offingers. However, it should be understood that principles disclosedherein may be applicable to transistor stacks comprising any number oftransistors and/or transistors having any number of fingers, and eventransistors having a single gate, drain and/or source finger. In thetransistor stack 1400, each of the transistors Q₁-Q₄ may have similarcharacteristics and/or dimensions and may be designed to achieverelatively-low drain-to-source capacitance. However, in certainembodiments, wherein drain-to-source spacing is not placed at relativelyminimal values, which may provide relatively minimal totalmetal-to-metal capacitance, uneven voltage distribution may result, asdescribed above.

Certain dimensions of the transistor stack 1400 and transistors thereofare shown. However, it should be understood that such dimensions are notnecessarily drawn to scale and may have any desirable or suitable valuesand still fall within the scope of the present disclosure. Thetransistors Q₁-Q₄ may each have similar dimensions. Therefore, thedimensions of the transistor stack 1400 may be understood with referenceto Q₁ and/or Q₂, as diagrammed in FIG. 20A. In certain embodiments, Q₁may have a total area of approximately 2475 μm² and a total gate widthlength of approximately 2 mm. The total area of the transistor Q₁ may bebased on the width w₁ of the transistor multiplied by the total length Yof the transistor. The total gate “width” and/or “transistor periphery”may represent the aggregate length of all of the individual gate fingers(G_(1a)-G_(1n)) of the transistor Q₁. The total gate width of thetransistor may at least partially determine device performancecharacteristics, such as ON-resistance, which it may be desirable tomaintain at a relatively low level in certain situations. The gate widthmay be based on a finger count of approximately 133, or other number,with a finger width w₁ of approximately 15 μm. In certain embodiments,the drain-to-source spacing X_(DS) may be approximately 0.84 μm, with atotal drain-to-drain or source-to-source distance X_(DD) ofapproximately 1.68 μm. As explained above, references herein todrain-to-source spacing may further be representative of gate-to-gatespacing in certain embodiments.

The transistor Q₁, based on specifications similar to those listedabove, may have an ON-resistance of approximately 0.35 Ohm andOFF-capacitance of approximately 306 fF. Therefore, the combination ofOn-resistance and OFF-capacitance may be represented by Ron*Coff(fs)≈107.

FIG. 20B shows a side view of an example FET transistor according to oneor more embodiments. The transistor shown in FIG. 20B may berepresentative of the transistor Q₁ of FIG. 20A, for example. Thediagram of FIG. 20B shows the capacitance present between the drain andsource of the transistor Q₁, as described in greater detail above. FIG.20C shows a schematic depiction of the transistor stack of FIG. 20Aaccording to one or more embodiments, which shows the transistors Q₁-Q₄connected in series.

For reasons discussed in detail above, it may be desirable foradditional capacitance to be present from drain-to-source with respectto certain transistors in an RF transistor stack. Among possible ways inwhich such capacitance may be achieved, certain embodiments provide foradding capacitance to a transistor through the addition of metal to thevarious drain and/or source fingers of a transistor that may act asinterdigitated drain-to-source capacitors.

FIG. 21A shows a plan view of an example transistor stack according toone or more embodiments. The transistor stack 1500 may be similar incertain respects to the transistor stack 1400 shown in FIG. 20A. Withrespect to the transistor stack 1500, added capacitance for transistorsQ₁ and/or Q₂ may be provided through the addition of metal traces ondrain and/or source fingers. For example, transistor Q₁ includes a drainfinger D_(1a) that may have electrically coupled thereto a metal traceM_(D1), and a source finger S_(1a) that may have electrically coupledthereto a metal trace M_(S1). The metal trace M_(D1) may have a lengthL_(MD1), which may substantially span the entire length of the drainfinger, or a portion thereof. The metal trace MS1 may further have alength L_(MS1), which may likewise span the entire length of the sourcefinger, or merely a portion thereof. The length and/or thickness of thevarious metal traces may affect the amount of capacitance contributed bythe traces. The metal traces may comprise a stack of metal on top of therespective fingers. In certain embodiments, a stack of metal may alreadyexist on the wafer, and so implementing the metal traces of FIG. 21A maymerely involve patterning such metal.

In certain embodiments, metal traces (e.g., M_(D2), M_(S2)) may beassociated with the respective drain and/or source fingers of one ormore additional transistors of the stack 1500, such as with the adjacenttransistor Q₂. In certain embodiments, the desired capacitance added tothe subsequent transistor Q₂ may be less than the capacitance that isdesirable for Q₁. Therefore, the length of the metal trace(s) L_(MD2)associated with the drain D_(2b) of Q₂ may be less than the length ofthe corresponding traces of Q₁, and/or the length of the metal trace(s)L_(MS2) associated with the source S_(2b) of Q₂ may be less than thelength of the corresponding traces of Q₂.

FIG. 21B shows a side view of an example FET transistor according to oneor more embodiments. The transistor Q₁ of FIG. 21B includes metal tracesM_(D) and M_(S) coupled to the drain D and source S, respectively. Themetal includes vertical via portions 1501, 1502 which may electricallycouple metal between dielectric layers of the device. The capacitanceadded by the additional metal traces MD, MS is represented by thecapacitor C_(DS-UPPER), while the drain-to-source capacitance from thefirst layer of interconnect metal is represented by C_(DS-LOWER).

FIG. 21C shows a schematic depiction of the transistor stack of FIG. 21Aaccording to one or more embodiments. The capacitors C_(M1), C_(M2)represent the added capacitance provided by the additional metal traces.In addition to the additional metal traces described in connection withFIGS. 21A-21C, added drain-to-source capacitance may be achieved usingvarious other mechanisms as well. For example, in certain embodiments,drain and/or source metals may be widened, thereby bringing the drainand source relatively closer together, which may increasedrain-to-source capacitance. However, similarly to the metal tracesolution, such solution may generally be applied on a transistor (e.g.,FET) stack where all transistors have similar, or uniform,drain-to-source spacing. Certain embodiments disclosed herein mayachieve added capacitance through non-uniform drain-to-source spacing asan alternative to other capacitance adding techniques, or in additionthereto.

FIG. 22A shows a plan view of an example transistor stack 1600 accordingto one or more embodiments. The transistor stack 1600 may includenon-uniform, or variable, drain-to-source (and/or gate-to-gate) spacing,as referenced above. In certain embodiments, where the drain-to-sourcecapacitance for a selected transistor (e.g., Q₁) of a transistor stackis desired to be relatively high compared to one or more othertransistors of the stack, such higher capacitance may be achievedthrough relative reduction of drain-to-source (and/or gate-to-gate)spacing as an alternative to, or in addition to, adding additionalmetal. Such a configuration may result in a stack of transistors whereeach of transistors, or subsets of transistors, have differentdrain-to-source (and/or gate-to-gate) spacing. In such embodiments,added capacitance may be achieved while simultaneously reducing sizeand/or loss.

Certain dimensions of the transistor stack 1600 and transistors thereofare shown. However, it should be understood that such dimensions are notnecessarily drawn to scale and may have any desirable or suitable valuesand still fall within the scope of the present disclosure. In theembodiment of FIG. 22A, the total transistor peripheries may be similarto a transistor stack such as that shown in FIG. 20A and describedabove, wherein additional capacitance is achieved through reduceddrain-to-source spacing and reduced size is also achieved due to thereduced spacing. That is, with the drain-to-source (and/or gate-to-gate)spacing of at least one of the transistors (e.g., Q₁) being reduced,more fingers may fit within the length Y of the transistor, andtherefore, the same periphery may be achieved with a reduced unit gatewidth w₁, thereby reducing the overall footprint of the transistor Q₁and/or transistor stack 1600.

Reducing the drain-to-source (and/or gate-to-gate) spacing, as shown forQ₁ relative to Q3 and Q4, may cause the existing metal layers to bebrought closer to each other, thereby increasing capacitance and/orallowing for more fingers to fit within the width dimension Y, which mayallow for a smaller unit gate width dimension w₁ relative to a unit gatewidth w₂ of the adjacent transistor Q₂ of the stack 1600. In addition,the unit gate width w₂ of the transistor Q₂ may be smaller than the nextadjacent transistor Q₃ of the stack 1600. In certain embodiments, theunit gate width w₃ of the transistor Q₃ may be substantially equal tothe unit gate width w₄ of the next adjacent transistor Q₄ of the stack1600. That is, while some of the transistors may have relatively smallerunit gate widths, or graduated unit gate widths, multiple transistorsfarther down the stack may have similar unit gate widths. The smallerdimension w₁ can result in a smaller and/or cheaper die, as well asincreased capacitance associated with one or more transistors. With thetotal transistor periphery maintained, the solution of FIG. 22A mayfurther provide similar ON-resistance characteristics compared tocertain larger device implementations.

In the embodiment of FIG. 22A, rather than adding features to certaintransistors in a uniform stack of transistors to obtain variablecapacitance, the geometry of the base transistor Q₁ and/or one or moreadditional transistors (e.g., Q₂) may be modified to provide certainadditional side benefits, such as reduced size and/or reduced loss, inaddition to the desired added non-uniform capacitance. In certainembodiments, the drain-to-source distance X_(DS1) for a transistor(e.g., Q₁) of the stack 1600 may be reduced relative to thecorresponding distance of one or more other transistors of the stack toapproximately 0.76 μm, with a total drain-to-drain or source-to-sourcedistance X_(DD1) of approximately 1.52 μm. As explained above,references herein to drain-to-source spacing may further berepresentative of gate-to-gate spacing in certain embodiments.

The individual unit gate width w₁ of the transistor Q₁ may beapproximately 14.0 μm in certain embodiments. In certain embodiments,the unit gate width w₁ associated with transistor Q₁ may be at least 5%shorter than that of one or more other transistors of the stack 1600.For example, the unit gate width w₁ of transistor Q₁ may beapproximately 6.67% shorter than the unit gate width w₄ of transistor Q₄and/or that of one or more other transistors (e.g., Q₃). The total gatewidth for the transistor Q₁ may be maintained at least in part byincreasing the number of gate, drain and/or source fingers, such thatthe total dimension X of the stack and dimension w₁ of the transistor Q₁are reduced, while the dimension Y of the stack may be substantiallymaintained in certain embodiments, thereby providing a reduced totalarea for the transistor Q₁ and/or transistor stack 1600.

In certain embodiments, the total number of gate fingers of thetransistor Q₁ may be approximately 143, which may be more than thatassociated with another of the transistors of the stack 1600, such astransistor Q₄, which may have approximately 133 total gate fingers, forexample.

With further reference to FIG. 22A, The total gate width, or periphery,of the transistor Q₁ may be approximately 2000 μm according to certainembodiments, which may be based on a drain-to-source length X_(DS1) ofapproximately 0.76, or less. In certain embodiments, the drain-to-sourcelength X_(DS1) is between approximately 0.76-0.84. In certainembodiments, the drain-to-source length X_(DS1) of the transistor Q₁ isat least approximately 8% less than the drain-to-source length (e.g.,X_(DS4)) associated with another transistor (e.g., Q₄) of the stack1600. In certain embodiments, the drain-to-source length X_(DS1) of thetransistor Q₁ is at least approximately 9% less than the drain-to-sourcelength (e.g., X_(DS4)) associated with another transistor (e.g., Q₄) ofthe stack 1600. For example, the drain-to-source length X_(DS1) of thetransistor Q₁ may be at least approximately 10% less than thedrain-to-source length (e.g., X_(DS4)) associated with anothertransistor (e.g., Q₄) of the stack 1600.

According to the example dimensions presented immediately above, thetransistor Q₁ may have an ON-resistance of approximately 0.35 Ohm, whichmay represent substantially no reduction or increase in ON-resistancewith respect to certain other transistors (e.g., Q₄) of the transistorstack 1600, or compared to a transistor of certain other transistorstacks having uniform drain-to-source spacing. The transistor Q₁ mayhave an OFF-capacitance of approximately 338 fF, which may represent acapacitance approximately 10% greater than one or more other transistors(e.g., Q₄) of the stack 1600 or compared to a transistor of certainother transistor stacks having uniform drain-to-source spacing.Therefore, the combination of ON-resistance and OFF-capacitance may berepresented by Ron*Coff (fs)≈118. In certain embodiments, the transistorQ₁ may have an area of approximately 2313 μm², which may represent areduction in transistor area of approximately 7% compared to one or moreother transistors (e.g., Q₄) of the stack 1600 or compared to atransistor of certain other transistor stacks having uniformdrain-to-source spacing.

With further reference to FIG. 22A, the drain-to-source (and/orgate-to-gate) spacing X_(DS2) of the adjacent transistor Q₂ may begreater than that of transistor Q₁, but may still represent a reduceddrain-to-source spacing with respect to one or more other transistors(e.g., Q₃ and/or Q₄) of the stack 1600. The gate length w₂ of thetransistor Q₂ may be greater than the gate length w₁ of transistor Q₁,but less than the gate length w₃, w₄ of one or more other transistors(e.g., Q₃, Q₄) of the stack 1600. In certain embodiments, thedrain-to-source spacing X_(DS3) of the transistor Q₃ may besubstantially equal to the drain-to-source spacing X_(DS4) of the nextadjacent transistor Q₄ of the stack 1600. That is, while some of thetransistors may have relatively smaller drain-to-source spacing, orgraduated drain-to-source spacing, multiple transistors farther down thestack may have similar drain-to-source spacing.

The relative and/or actual dimensions shown in FIG. 22A and describedabove may be fabricated using a patterned mask having a form designed toproduce the various features and/or dimensions disclosed.

FIG. 22B shows a side view of an example FET transistor Q₁ according toone or more embodiments. The transistor Q₁ of FIG. 21B may correspond toa transistor having reduced relative unit gate width and/ordrain-to-source spacing as shown in FIG. 22A. The capacitance added byvirtue of the reduced drain-to-source spacing is represented by thecapacitor C_(DS-A), while the original drain-to-source capacitance fromthe FET Q₁ of FIG. 20A is represented by C_(DS).

FIG. 22C shows a schematic depiction of the transistor stack of FIG. 22Aaccording to one or more embodiments. The capacitors C_(A1), C_(A2)represent the added capacitance provided by reduced unit gate widthand/or drain-to-source spacing.

FIG. 23 shows a plan view of an example transistor stack 1700 accordingto one or more embodiments. Certain dimensions of the transistor stack1400 and transistors thereof are shown. However, it should be understoodthat such dimensions are not necessarily drawn to scale and may have anydesirable or suitable values and still fall within the scope of thepresent disclosure. The transistor Q₁ of the stack 1700 may differ fromthe transistor Q₁ of the stack 1600 of FIG. 22A in that the transistorQ₁ of FIG. 23 may not have relatively reduce unit gate width w₁ comparedto other transistors (e.g., Q₄) of the stack 1700. However, thetransistor Q₁ of FIG. 23 includes reduced relative drain-to-sourcespacing X_(DS1). Such a configuration may provide increased totaltransistor periphery, which may result in reduced ON-resistance and/orreduced loss, while substantially maintaining transistor size. Thereduced drain-to-source spacing may increase the capacitance oftransistor Q₁ with respect to other transistors in the stack 1700 thathave greater drain-to-source spacing. As explained above, referencesherein to drain-to-source spacing may further be representative ofgate-to-gate spacing in certain embodiments.

Due to the reduced drain-to-source (and/or gate-to-gate) spacing thetransistor Q₁ may be able to accommodate an increased number of gate,source and/or drain fingers compared to one or more other transistors ofthe stack 1700, which provides a relatively greater periphery for thetransistor Q₁, which may further lead to reduced ON-resistance and/orimproved performance from an ON-resistance perspective. Furthermore,increased capacitance may be achieved without suffering from increasedtransistor/stack size compared to certain transistor stacks havinguniform drain-to-source distance across transistors of a stack.

In one embodiment of FIG. 23, rather than adding features to certaintransistors in a uniform stack of transistors to obtain variablecapacitance, the geometry of the base transistor Q₁ and/or one or moreadditional transistors (e.g., Q₂) may be modified to provide certainadditional side benefits, such as reduced loss, in addition to thedesired added non-uniform capacitance. In certain embodiments, thedrain-to-source (and/or gate-to-gate) distance X_(DS1) for a transistor(e.g., Q₁) of the stack 1700 may be reduced relative to thecorresponding distance of one or more other transistors of the stack toapproximately 0.76 μm, with a total drain-to-drain or source-to-sourcedistance X_(DD1) of approximately 1.52 μm. The individual unit gatewidth w₁ of the transistor Q₁ may be approximately 15.1 μm in certainembodiments. The total gate width for the transistor Q₁ may be greaterthan that of one or more additional transistors (e.g., Q₄) of the stack1700 due to the decreased drain-to-source (and/or gate-to-gate) spacing,which may allow for additional gate, source and/or drain fingers to befit within the dimensions of the transistor. In certain embodiments, thetotal number of gate fingers of the transistor Q₁ may be approximately143, which may be more than that associated with another of thetransistors of the stack 1700, such as transistor Q₄, which may haveapproximately 133 total gate fingers, for example.

With further reference to FIG. 23, in one embodiment, the total gatewidth, or periphery, of the transistor Q1 may be approximately 2159 μmaccording to certain embodiments, which may be based on adrain-to-source X_(DS1) length of approximately 0.76, or less. Incertain embodiments, the drain-to-source length X_(DS1) is betweenapproximately 0.76-0.84. In certain embodiments, the drain-to-sourcelength X_(DS1) of the transistor Q₁ is at least approximately 8% lessthan the drain-to-source length (e.g., X_(DS4)) associated with anothertransistor (e.g., Q₄) of the stack 1700. In certain embodiments, thedrain-to-source length X_(DS1) of the transistor Q₁ is at leastapproximately 9% less than the drain-to-source length (e.g., X_(DS4))associated with another transistor (e.g., Q₄) of the stack 1700. Forexample, the drain-to-source length X_(DS1) of the transistor Q₁ may beat least approximately 10% less than the drain-to-source length (e.g.,X_(DS4)) associated with another transistor (e.g., Q₄) of the stack1700.

With further reference to FIG. 23, according to the example dimensionspresented immediately above, the transistor Q₁ may have an ON-resistanceof approximately 0.32 Ohm, which may represent a reduction ofapproximately 8% or more with respect to certain other transistors(e.g., Q₄) of the transistor stack 1700, or compared to a transistor ofcertain other transistor stacks having uniform drain-to-source spacing.The transistor Q₁ may have an OFF-capacitance of approximately 365 fF,which may represent a capacitance approximately 19% greater than one ormore other transistors (e.g., Q₄) of the stack 1700 or compared to atransistor of certain other transistor stacks having uniformdrain-to-source spacing. The combination of ON-resistance andOFF-capacitance may be represented by Ron*Coff (fs)≈118. In certainembodiments, the transistor Q₁ may have an area of approximately 2474μm², which may represent a substantially uniform transistor areacompared to one or more other transistors (e.g., Q₄) of the stack 1700or compared to a transistor of certain other transistor stacks havinguniform drain-to-source spacing. With further reference to FIG. 23, Thedrain-to-source (and/or gate-to-gate) spacing X_(DS2) may be greaterthan that of transistor Q₁, but may still represent a reduceddrain-to-source spacing with respect to one or more other transistors(e.g., Q₃ and/or Q₄) of the stack 1700.

In another embodiment of the transistor stack 1700 FIG. 23, thedrain-to-source distance X_(DS1) for a transistor (e.g., Q₁) of thestack 1700 may be reduced relative to the corresponding distance of oneor more other transistors of the stack to approximately 0.8 μm, with atotal drain-to-drain or source-to-source distance X_(DD1) ofapproximately 1.6 μm. The individual unit gate width W₁ of thetransistor Q₁ may be approximately 15.1 μm in certain embodiments. Thetotal gate width for the transistor Q₁ may be greater than that of oneor more additional transistors (e.g., Q₄) of the stack 1700 due to thedecreased drain-to-source (and/or gate-to-gate) spacing, which may allowfor additional gate, source and/or drain fingers to be fit within thedimensions of the transistor. In certain embodiments, the total numberof gate fingers of the transistor Q₁ may be approximately 137, which maybe more than that associated with another of the transistors of thestack 1700, such as transistor Q₄, which may have approximately 133total gate fingers, for example.

With further reference to FIG. 23, in one embodiment, the total gatewidth, or periphery, of the transistor Q1 may be approximately 2069 μmaccording to certain embodiments, which may be based on adrain-to-source length X_(DS1) of approximately 0.8, or less. In certainembodiments, the drain-to-source length X_(DS1) is between approximately0.80-0.84. In certain embodiments, the drain-to-source (and/orgate-to-gate) length X_(DS1) of the transistor Q₁ is at leastapproximately 4% less than the drain-to-source (and/or gate-to-gate)length (e.g., X_(DS4)) associated with another transistor (e.g., Q₄) ofthe stack 1700. In certain embodiments, the drain-to-source (and/orgate-to-gate) length X_(DS1) of the transistor Q₁ is at leastapproximately 4.7% less than the drain-to-source (and/or gate-to-gate)length (e.g., X_(DS4)) associated with another transistor (e.g., Q₄) ofthe stack 1700.

With further reference to FIG. 23, according to the example dimensionspresented immediately above, the transistor Q₁ may have an ON-resistanceof approximately 0.34 Ohm, which may represent a reduction ofapproximately 3% or more with respect to certain other transistors(e.g., Q₄) of the transistor stack 1700, or compared to a transistor ofcertain other transistor stacks having uniform drain-to-source spacing.The transistor Q₁ may have an OFF-capacitance of approximately 332 fF,which may represent a capacitance approximately 8% greater than one ormore other transistors (e.g., Q₄) of the stack 1700 or compared to atransistor of certain other transistor stacks having uniformdrain-to-source spacing. The combination of ON-resistance andOFF-capacitance may be represented by Ron*Coff (fs)≈113. In certainembodiments, the transistor Q₁ may have an area of approximately 2464μm², which may represent a substantially uniform transistor areacompared to one or more other transistors (e.g., Q₄) of the stack 1700or compared to a transistor of certain other transistor stacks havinguniform drain-to-source spacing. With further reference to FIG. 23, Thedrain-to-source spacing X_(DS2) may be greater than that of transistorQ₁, but may still represent a reduced drain-to-source spacing withrespect to one or more other transistors (e.g., Q₃ and/or Q₄) of thestack 1700. In certain embodiments, the drain-to-source spacing X_(DS3)of the transistor Q₃ may be substantially equal to the drain-to-sourcespacing X_(DS4) of the next adjacent transistor Q₄ of the stack 1700.That is, while some of the transistors may have relatively smallerdrain-to-source spacing, or graduated drain-to-source spacing, multipletransistors farther down the stack may have similar drain-to-sourcespacing.

The relative and/or actual dimensions shown in FIG. 23 and describedabove may be fabricated using a patterned mask having a form designed toproduce the various features and/or dimensions disclosed.

Examples Related to Switch Configurations

As described herein in reference to the examples of FIGS. 13-17, FETdevices having one or more features of the present disclosure can beutilized to implement an SPDT switch configuration. It will beunderstood that FET devices having one or more features of the presentdisclosure can also be implemented in other switch configurations.

FIGS. 24-34 show examples related to various switch configurations thatcan be implemented utilizing FET devices such as SOI FET devices havingone or more features as described herein. For example, FIG. 24 shows aswitch assembly 250 implemented in a single-pole-single-throw (SPST)configuration. Such a switch can include an SOI FET device 100implemented between a first port (Port1) and a second port (Port2).

FIG. 25 shows that in some embodiments, the SOI FET device 100 of FIG.24 can include a substrate biasing/coupling feature as described herein.The source node of the SOI FET device 100 can be connected to the firstport (Port1), and the drain node of the SOI FET device 100 can beconnected to the second port (Port2). As described herein, the SOI FETdevice 100 can be turned ON to close the switch 250 (of FIG. 24) betweenthe two ports, and turned OFF to open the switch 250 between the twoports.

It will be understood that the SOI FET device 100 of FIGS. 24 and 25 caninclude a single FET, or a plurality of FETs arranged in a stack. Itwill also be understood that each of various SOI FET devices 100 ofFIGS. 26-34 can include a single FET, or a plurality of FETs arranged ina stack.

FIG. 26 shows an example of how two SPST switches (e.g., similar to theexamples of FIGS. 24, 25) having one or more features as describedherein can be utilized to form a switch assembly 250 having asingle-pole-double-throw (SPDT) configuration. FIG. 27 shows, in a SPDTrepresentation, that the switch assembly 250 of FIG. 26 can be utilizedin an antenna switch configuration 260. It will be understood that oneor more features of the present disclosure can also be utilized inswitching applications other than antenna switching application.

It is noted that in various switching configuration examples of FIGS.24-34, switchable shunt paths are not shown for simplified views of theswitching configurations. Accordingly, it will be understood that someor all of switchable paths in such switching configurations may or maynot have associated with them switchable shunt paths.

Referring to the examples of FIGS. 26 and 27, it is noted that suchexamples may be similar to the examples described herein in reference toFIGS. 13-15. In some embodiments, the single pole (P) of the switchassembly 250 of FIG. 26 can be utilized as an antenna node (Ant) of theantenna switch 260, and the first and second throws (T1, T2) of theswitch assembly 250 of FIG. 26 can be utilized as TRx1 and TRx2 nodes,respectively, of the antenna switch 260. Although each of the TRx1 andTRx2 nodes is indicated as providing transmit (Tx) and receive (Rx)functionalities, it will be understood that each of such nodes can beconfigured to provide either or both of such Tx and Rx functionalities.

In the examples of FIGS. 26 and 27, the SPDT functionality is shown tobe provided by two SPST switches 100 a, 100 b, with the first SPSTswitch 100 a providing a first switchable path between the pole P (Antin FIG. 27) and the first throw T1 (TRx1 in FIG. 27), and the secondSPST switch 100 b providing a second switchable path between the pole P(Ant in FIG. 27) and the second throw T2 (TRx2 in FIG. 27). Accordingly,selective coupling of the pole (Ant) with either of the first throw T1(TRx1) and the second throw T2 (TRx2) can be achieved by selectiveswitching operations of the first and second SPST switches. For example,if a connection is desired between the pole (Ant) and the first throw T1(TRx1), the first SPST switch 100 a can be closed, and the second SPSTswitch 100 b can be opened. Similarly, and as depicted in the examplestate in FIGS. 26 and 27, if a connection is desired between the pole(Ant) and the second throw T2 (TRx2), the first SPST switch 100 a can beopened, and the second SPST switch 100 b can be closed.

In the foregoing switching examples of FIGS. 26 and 27, a single TRxpath is connected to the antenna (Ant) node in a given switchconfiguration. It will be understood that in some applications (e.g.,carrier-aggregation applications), more than one TRx paths may beconnected to the same antenna node. Thus, in the context of theforegoing switching configuration involving a plurality of SPSTswitches, more than one of such SPST switches can be closed to therebyconnect their respective throws (TRx nodes) to the same pole (Ant).

FIG. 28 shows an example of how three SPST switches (e.g., similar tothe examples of FIGS. 24, 25) having one or more features as describedherein can be utilized to form a switch assembly 250 having asingle-pole-triple-throw (SP3T) configuration. FIG. 29 shows, in a SP3Trepresentation, that the switch assembly 250 of FIG. 29 can be utilizedin an antenna switch configuration 260. It will be understood that oneor more features of the present disclosure can also be utilized inswitching applications other than antenna switching application.

Referring to the examples of FIGS. 28 and 29, it is noted that the SP3Tconfiguration can be an extension of the SPDT configuration of FIGS. 26and 27. For example, the single pole (P) of the switch assembly 250 ofFIG. 28 can be utilized as an antenna node (Ant) of the antenna switch260, and the first, second and third throws (T1, T2, T3) of the switchassembly 250 of FIG. 28 can be utilized as TRx1, TRx2 and TRx3 nodes,respectively, of the antenna switch 260. Although each of the TRx1, TRx2and TRx3 nodes is indicated as providing transmit (Tx) and receive (Rx)functionalities, it will be understood that each of such nodes can beconfigured to provide either or both of such Tx and Rx functionalities.

In the examples of FIGS. 28 and 29, the SP3T functionality is shown tobe provided by three SPST switches 100 a, 100 b, 100 c, with the firstSPST switch 100 a providing a first switchable path between the pole P(Ant in FIG. 29) and the first throw T1 (TRx1 in FIG. 29), the secondSPST switch 100 b providing a second switchable path between the pole P(Ant in FIG. 29) and the second throw T2 (TRx2 in FIG. 29), and thethird SPST switch 100 c providing a third switchable path between thepole P (Ant in FIG. 29) and the third throw T3 (TRx3 in FIG. 29).Accordingly, selective coupling of the pole (Ant) with one of the firstthrow T1 (TRx1), the second throw T2 (TRx2), and the third throw T3(TRx3) can be achieved by selective switching operations of the first,second and third SPST switches. For example, if a connection is desiredbetween the pole (Ant) and the first throw T1 (TRx1), the first SPSTswitch 100 a can be closed, and each of the second and third SPSTswitches 100 b, 100 c can be opened. If a connection is desired betweenthe pole (Ant) and the second throw T2 (TRx2), the second SPST switch100 b can be closed, and each of the first and third SPST switches 100a, 100 c can be opened. Similarly, and as depicted in the example statein FIGS. 28 and 29, if a connection is desired between the pole (Ant)and the third throw T3 (TRx3), each of the first and second SPSTswitches 100 a, 100 b can be opened, and the third SPST switch 100 c canbe closed.

In the foregoing switching examples of FIGS. 28 and 29, a single TRxpath is connected to the antenna (Ant) node in a given switchconfiguration. It will be understood that in some applications (e.g.,carrier-aggregation applications), more than one TRx paths may beconnected to the same antenna node. Thus, in the context of theforegoing switching configuration involving a plurality of SPSTswitches, more than one of such SPST switches can be closed to therebyconnect their respective throws (TRx nodes) to the same pole (Ant).

Based on the foregoing examples of SPST, SPDT and SP3T configurations ofFIGS. 24-29, one can see that other switching configurations involving asingle pole (SP) can be implemented utilizing SOI FET devices having oneor more features as described herein. Thus, it will be understood that aswitch having a SPNT can be implemented utilizing one or more SOI FETdevices as described herein, where the quantity N is a positive integer.

Switching configurations of FIGS. 26-29 are examples where a single pole(SP) is connectable to one or more of a plurality of throws to providethe foregoing SPNT functionality. FIGS. 30-33 show examples where morethan one poles can be provided in switching configurations. FIGS. 30 and31 show examples related to a double-pole-double-throw (DPDT) switchingconfiguration that can utilize a plurality of SOI FET devices having oneor more features as described herein. Similarly, FIGS. 32 and 33 showexamples related to a triple-pole-triple-throw (3P3T) switchingconfiguration that can utilize a plurality of SOI FET devices having oneor more features as described herein.

It will be understood that a switching configuration utilizing aplurality of SOI FET devices having one or more features as describedherein can include more than three poles. Further, it is noted that inthe examples of FIGS. 30-33, the number of throws (e.g., 2 in FIGS. 30and 31, and 3 in FIGS. 32 and 33) are depicted as being the same as thecorresponding number of poles for convenience. However, it will beunderstood that the number of throws may be different than the number ofpoles.

FIG. 30 shows an example of how four SPST switches (e.g., similar to theexamples of FIGS. 24, 25) having one or more features as describedherein can be utilized to form a switch assembly 250 having a DPDTconfiguration. FIG. 31 shows, in a DPDT representation, that the switchassembly 250 of FIG. 30 can be utilized in an antenna switchconfiguration 260. It will be understood that one or more features ofthe present disclosure can also be utilized in switching applicationsother than antenna switching application.

In the examples of FIGS. 30 and 31, the DPDT functionality is shown tobe provided by four SPST switches 100 a, 100 b, 100 c, 100 d. The firstSPST switch 100 a is shown to provide a switchable path between a firstpole P1 (Ant1 in FIG. 31) and a first throw T1 (TRx1 in FIG. 31), thesecond SPST switch 100 b is shown to provide a switchable path between asecond pole P2 (Ant2 in FIG. 31) and the first throw T1 (TRx1 in FIG.31), the third SPST switch 100 c is shown to provide a switchable pathbetween the first pole P1 (Ant1 in FIG. 31) and a second throw T2 (TRx2in FIG. 31), and the fourth SPST switch 100 d is shown to provide aswitchable path between the second pole P2 (Ant2 in FIG. 31) and thesecond throw T2 (TRx2 in FIG. 31). Accordingly, selective couplingbetween one or more of the poles (antenna nodes) with one or more of thethrows (TRx nodes) can be achieved by selective switching operations ofthe four SPST switches 100 a, 100 b, 100 c, 100 d. Examples of suchswitching operations are described herein in greater detail.

FIG. 32 shows an example of how nine SPST switches (e.g., similar to theexamples of FIGS. 24, 25) having one or more features as describedherein can be utilized to form a switch assembly 250 having a 3P3Tconfiguration. FIG. 33 shows, in a 3P3T representation, that the switchassembly 250 of FIG. 32 can be utilized in an antenna switchconfiguration 260. It will be understood that one or more features ofthe present disclosure can also be utilized in switching applicationsother than antenna switching application.

Referring to the examples of FIGS. 32 and 33, it is noted that the 3P3Tconfiguration can be an extension of the DPDT configuration of FIGS. 30and 31. For example, a third pole (P3) can be utilized as a thirdantenna node (Ant3), and a third throw (T3) can be utilized as a thirdTRx node (TRx3). Connectivity associated with such third pole and thirdthrow can be implemented similar to the examples of FIGS. 30 and 31.

In the examples of FIGS. 32 and 33, the 3P3T functionality is shown tobe provided by nine SPST switches 100 a-100 i. Such nine SPST switchescan provide switchable paths as listed in Table 1.

TABLE 1 SPST switch Pole Throw 100a P1 T1 100b P2 T1 100c P3 T1 100d P1T2 100e P2 T2 100f  P3 T2 100g P1 T3 100h P2 T3 100i  P3 T3

Based on the example of FIGS. 32 and 33, and Table 1, one can see thatselective coupling between one or more of the poles (antenna nodes) withone or more of the throws (TRx nodes) can be achieved by selectiveswitching operations of the nine SPST switches 100 a-100 i.

In many applications, switching configurations having a plurality ofpoles and a plurality of throws can provide increased flexibility in howRF signals can be routed therethrough. FIGS. 34A-34E show examples ofhow a DPDT switching configuration such as the examples of FIGS. 30 and31 can be operated to provide different signal routing functionalities.It will be understood that similar control schemes can also beimplemented for other switching configurations, such as the 3P3Texamples of FIGS. 32 and 33.

In some wireless front-end architectures, two antennas can be provided,and such antennas can operate with two channels, with each channel beingconfigured for either or both of Tx and Rx operations. For the purposeof description, it will be assumed that each channel is configured forboth Tx and Rx operations (TRx). However, it will be understood thateach channel does not necessarily need to have such TRx functionality.For example, one channel can be configured for TRx operations, while theother channel can be configured for Rx operation. Other configurationsare also possible.

In the foregoing front-end architectures, there may be relatively simpleswitching states including a first state and a second state. In thefirst state, the first TRx channel (associated with the node TRx1) canoperate with the first antenna (associated with the node Ant1), and thesecond TRx channel (associated with the node TRx2) can operate with thesecond antenna (associated with the node Ant2). In the second state,connections between the antenna nodes and the TRx nodes can be swappedfrom the first state. Accordingly, the first TRx channel (associatedwith the node TRx1) can operate with the second antenna (associated withthe node Ant2), and the second TRx channel (associated with the nodeTRx2) can operate with the first antenna (associated with the nodeAnt1).

In some embodiments, such two states of the DPDT switching configurationcan be controlled by a one-bit logic scheme, as shown in the examplelogic states in Table 2.

TABLE 2 Control TRx1-Ant1 TRx1-Ant2 TRx2-Ant1 TRx2-Ant2 State logicconnection connection connection connection 1 0 Yes No No Yes 2 1 No YesYes No

The first state (State 1) of the example of Table 2 is depicted in FIG.34A as 270 a, where the TRx1-Ant1 connection is indicated as path 274 a,and the TRx2-Ant2 connection is indicated as path 276 a. A controlsignal, representative of the control logic of Table 2, provided to theassembly (272) of the four SPST switches (100 a, 100 b, 100 c, 100 d) iscollectively indicated as Vc(s). Similarly, the second state (State 2)of the example of Table 2 is depicted in FIG. 34B as 270 b, where theTRx1-Ant2 connection is indicated as path 276 b, and the TRx2-Ant1connection is indicated as path 274 b.

In some front-end architectures having a DPDT switching configuration,it may be desirable to have additional switching states. For example, itmay be desirable to have only one path active among the two TRx channelsand the two antennas. In another example, it may be desirable to disableall signal paths through the DPDT switch. Examples of 3-bit controllogic that can be utilized to achieve such examples switching states arelisted in Table 3.

TABLE 3 Control logic (Vc1, Vc2, TRx1-Ant1 TRx1-Ant2 TRx2-Ant1 TRx2-Ant2State Vc3) connection connection connection connection 1 0, 0, 0 No NoNo No 2 0, 0, 1 Yes No No Yes 3 0, 1, 0 Yes No No No 4 0, 1, 1 No YesYes No 5 1, 0, 0 No Yes No No

The first state (State 1) of the example of Table 3 is depicted in FIG.34E as 270 e, where all of the TRx-Ant paths are disconnected. A controlsignal indicated as Vc(s) in FIG. 34E and as listed in Table 3 can beprovided to the assembly (272) of the four SPST switches (100 a, 100 b,100 c, 100 d) to effectuate such a switching state.

The second state (State 2) of the example of Table 3 is depicted in FIG.34A as 270 a, where the TRx1-Ant1 connection is indicated as path 274 a,and the TRx2-Ant2 connection is indicated as path 276 a. A controlsignal indicated as Vc(s) in FIG. 34A and as listed in Table 3 can beprovided to the assembly (272) of the four SPST switches (100 a, 100 b,100 c, 100 d) to effectuate such a switching state.

The third state (State 3) of the example of Table 3 is depicted in FIG.34C as 270 c, where the TRx1-Ant1 connection is indicated as path 274 c,and all other paths are disconnected. A control signal indicated asVc(s) in FIG. 34C and as listed in Table 3 can be provided to theassembly (272) of the four SPST switches (100 a, 100 b, 100 c, 100 d) toeffectuate such a switching state.

The fourth state (State 4) of the example of Table 3 is depicted in FIG.34B as 270 b, where the TRx1-Ant2 connection is indicated as path 276 b,and the TRx2-Ant1 connection is indicated as path 274 b. A controlsignal indicated as Vc(s) in FIG. 34B and as listed in Table 3 can beprovided to the assembly (272) of the four SPST switches (100 a, 100 b,100 c, 100 d) to effectuate such a switching state.

The fifth state (State 5) of the example of Table 3 is depicted in FIG.34D as 270 d, where the TRx1-Ant2 connection is indicated as path 276 d,and all other paths are disconnected. A control signal indicated asVc(s) in FIG. 34D and as listed in Table 3 can be provided to theassembly (272) of the four SPST switches (100 a, 100 b, 100 c, 100 d) toeffectuate such a switching state.

As one can see, other switching configurations can also be implementedwith the DPDT switch of FIGS. 34A-34E. It will also be understood thatother switches such as 3P3T of FIGS. 32 and 33 can be controlled bycontrol logic in a similar manner.

Examples of Implementations in Products

In some embodiments, one or more die having one or more featuresdescribed herein can be implemented in a packaged module. An example ofsuch a module is shown in FIGS. 35A (plan view) and 35B (side view). Amodule 810 is shown to include a packaging substrate 812. Such apackaging substrate can be configured to receive a plurality ofcomponents, and can include, for example, a laminate substrate. Thecomponents mounted on the packaging substrate 812 can include one ormore dies. In the example shown, a die 800 having integrated active andpassive devices, as described herein, is shown to be mounted on thepackaging substrate 812. The die 800 can be electrically connected toother parts of the module (and with each other where more than one dieis utilized) through connections such as connection-wirebonds 816. Suchconnection-wirebonds can be formed between contact pads 818 formed onthe die 800 and contact pads 814 formed on the packaging substrate 812.In some embodiments, one or more surface mounted devices (SMDs) 822 canbe mounted on the packaging substrate 812 to facilitate variousfunctionalities of the module 810.

In some embodiments, the packaging substrate 812 can include electricalconnection paths for interconnecting the various components with eachother and/or with contact pads for external connections. For example, aconnection path 832 is depicted as interconnecting the example SMD 822and the die 800. In another example, a connection path 832 is depictedas interconnecting the SMD 822 with an external-connection contact pad834. In yet another example a connection path 832 is depicted asinterconnecting the die 800 with ground-connection contact pads 836.

In some embodiments, a space above the packaging substrate 812 and thevarious components mounted thereon can be filled with an overmoldstructure 830. Such an overmold structure can provide a number ofdesirable functionalities, including protection for the components andwirebonds from external elements, and easier handling of the packagedmodule 810.

FIG. 36 shows a schematic diagram of an example switching configurationthat can be implemented in the module 810 described in reference toFIGS. 35A and 35B. Although described in the context of a switch circuitand the bias/coupling circuit being on the same die (e.g., exampleconfiguration of FIG. 35A), it will be understood that packaged modulescan be based on other configurations. In the example, the switch circuit120 is depicted as being an SP9T switch, with the pole being connectableto an antenna and the throws being connectable to various Rx and Txpaths. Such a configuration can facilitate, for example, multi-modemulti-band operations in wireless devices.

The module 810 can further include an interface for receiving power(e.g., supply voltage VDD) and control signals to facilitate operationof the switch circuit 120 and/or the bias/coupling circuit 150. In someimplementations, supply voltage and control signals can be applied tothe switch circuit 120 via the bias/coupling circuit 150.

Wireless Device Implementation

In some implementations, a device and/or a circuit having one or morefeatures described herein can be included in an RF device such as awireless device. Such a device and/or a circuit can be implementeddirectly in the wireless device, in a modular form as described herein,or in some combination thereof. In some embodiments, such a wirelessdevice can include, for example, a cellular phone, a smart-phone, ahand-held wireless device with or without phone functionality, awireless tablet, etc.

FIG. 37 schematically depicts an example wireless device 900 having oneor more advantageous features described herein. In the context ofvarious switches and various biasing/coupling configurations asdescribed herein, a switch 120 and a bias/coupling circuit 150 can bepart of a module 919, which may include integrated active and passivedevices in accordance with one or more of the IPD processing on SOIlayer transfer substrate processes and embodiments disclosed herein.Furthermore, other components of the device 900 may include integratedactive/passive die(s) as described herein, such as the power amplifiermodule 914, duplexer 920 and/or other components or combinationsthereof. In some embodiments, the switch module 919 can facilitate, forexample, multi-band multi-mode operation of the wireless device 900.

In the example wireless device 900, a power amplifier (PA) module 916having a plurality of PAs can provide an amplified RF signal to theswitch 120 (via a duplexer 920), and the switch 120 can route theamplified RF signal to an antenna. The PA module 916 can receive anunamplified RF signal from a transceiver 914 that can be configured andoperated in known manners. The transceiver can also be configured toprocess received signals. The transceiver 914 is shown to interact witha baseband sub-system 910 that is configured to provide conversionbetween data and/or voice signals suitable for a user and RF signalssuitable for the transceiver 914. The transceiver 914 is also shown tobe connected to a power management component 906 that is configured tomanage power for the operation of the wireless device 900. Such a powermanagement component can also control operations of the basebandsub-system 910 and the module 919.

The baseband sub-system 910 is shown to be connected to a user interface902 to facilitate various input and output of voice and/or data providedto and received from the user. The baseband sub-system 910 can also beconnected to a memory 904 that is configured to store data and/orinstructions to facilitate the operation of the wireless device, and/orto provide storage of information for the user.

In some embodiments, the duplexer 920 can allow transmit and receiveoperations to be performed simultaneously using a common antenna (e.g.,924). In FIG. 37, received signals are shown to be routed to “Rx” paths(not shown) that can include, for example, a low-noise amplifier (LNA).

A number of other wireless device configurations can utilize one or morefeatures described herein. For example, a wireless device does not needto be a multi-band device. In another example, a wireless device caninclude additional antennas such as diversity antenna, and additionalconnectivity features such as Wi-Fi, Bluetooth, and GPS.

General Comments

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Description using the singularor plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While some embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A radio-frequency switch comprising: a firstfield-effect transistor having a first source finger, a first drainfinger, and a first gate finger interposed therebetween, the firstsource finger and the first drain finger being separated by a firstdrain-to-source distance; and a second field-effect transistor in aseries connection with the first field-effect transistor, the secondfield-effect transistor having a second source finger, a second drainfinger, and a second gate finger interposed therebetween, the secondsource finger and the second drain finger being separated by a seconddrain-to-source distance that is different than the firstdrain-to-source distance.
 2. The radio-frequency switch of claim 1wherein the second drain-to-source distance is greater than the firstdrain-to-source distance.
 3. The radio-frequency switch of claim 1further comprising a third field-effect transistor in a seriesconnection with the second field-effect transistor, the thirdfield-effect transistor having a third source finger, a third drainfinger, and a third gate finger interposed therebetween, the thirdsource finger and the third drain finger being separated by a thirddrain-to-source distance that is different than both the first andsecond drain-to-source distances.
 4. The radio-frequency switch of claim1 wherein the first and second field-effect transistors aresilicon-on-insulator transistors.
 5. The radio-frequency switch of claim1 wherein the first gate finger has a gate width that is shorter than agate width of the second gate finger.
 6. The radio-frequency switch ofclaim 1 wherein the first field-effect transistor occupies a smallerphysical area than the second field-effect transistor.
 7. Aradio-frequency module comprising: a first field-effect transistorhaving a first plurality of source fingers, a first plurality of drainfingers, and a first plurality of gate fingers including a gate fingerdisposed between each adjacent pair of source and drain fingers of thefirst plurality of drain fingers and the first plurality of sourcefingers, each of the first plurality of source fingers being separatedfrom an adjacent drain finger of the first plurality of drain fingers bya first drain-to-source distance; and a second field-effect transistorin a series connection with the first field-effect transistor, thesecond field-effect transistor having a second plurality of sourcefingers, a second plurality of drain fingers, and a second plurality ofgate fingers including a gate finger disposed between each adjacent pairof source and drain fingers of the second plurality of drain fingers andthe second plurality of source fingers, each of the second plurality ofsource fingers being separated from an adjacent drain finger of thesecond plurality of drain fingers by a second drain-to-source distancethat is different than the first drain-to-source distance.
 8. Theradio-frequency module of claim 7 wherein the second drain-to-sourcedistance is greater than the first drain-to-source distance.
 9. Theradio-frequency module of claim 7 further comprising a thirdfield-effect transistor in a series connection with the secondfield-effect transistor, the third field-effect transistor having athird plurality of source fingers, a third plurality of drain fingers,and a third plurality of gate fingers including a gate finger disposedbetween each adjacent pair of source and drain fingers of the thirdplurality of drain fingers and the third plurality of source fingers,each of the third plurality of source fingers being separated from anadjacent drain finger of the third plurality of drain fingers by a thirddrain-to-source distance that is different than both the first andsecond drain-to-source distances.
 10. The radio-frequency module ofclaim 9 wherein the second plurality of gate fingers has a gate widththat is longer than a gate width of the first plurality of gate fingersand shorter than a gate width of the third plurality of gate fingers.11. The radio-frequency module of claim 9 further comprising a fourthfield-effect transistor in a series connection with the thirdfield-effect transistor, the fourth field-effect transistor having afourth plurality of source fingers, a fourth plurality of drain fingers,and a fourth plurality of gate fingers including a gate finger disposedbetween each adjacent pair of source and drain fingers of the fourthplurality of drain fingers and the fourth plurality of source fingers,each of the fourth plurality of source fingers being separated from anadjacent drain finger of the fourth plurality of drain fingers by afourth drain-to-source distance that is equal to third distance.
 12. Theradio-frequency module of claim 7 wherein the first plurality of gatefingers comprises more gate fingers than the second plurality of gatefingers.
 13. The radio-frequency module of claim 7 wherein the firstplurality of gate fingers has a first gate width that is shorter than asecond gate width of the second plurality of gate fingers.
 14. Theradio-frequency module of claim 7 wherein the first field-effecttransistor has a total periphery that is greater than a total peripheryof the second field-effect transistor.
 15. The radio-frequency module ofclaim 7 wherein at least some of the first plurality of drain fingershave metal traces electrically coupled thereto to provide addedcapacitance.
 16. The radio-frequency module of claim 7 wherein the firstfield-effect transistor occupies a smaller physical area than the secondfield-effect transistor.
 17. The radio-frequency module of claim 7wherein the first field-effect transistor has a physical area equal to aphysical area of the second field-effect transistor.
 18. A method offabricating a transistor stack comprising: forming a first field-effecttransistor on a semiconductor substrate, the first field-effecttransistor having a first drain-to-source spacing; and forming a secondfield-effect transistor on the semiconductor substrate in a seriesconnection with the first field-effect transistor, the secondfield-effect transistor having a second drain-to-source spacing that isgreater than the first drain-to-source spacing.
 19. The method of claim18 further comprising forming a third field-effect transistor on thesemiconductor substrate, the third field-effect transistor having athird drain-to-source spacing that is greater than the seconddrain-to-source spacing.
 20. The method of claim 18 wherein the firstfield-effect transistor has a gate width that is shorter than a gatewidth of the second field-effect transistor.